The present invention relates to an optical element used in the field of optical communication and a method for aligning an optical fiber, laser diode chip or photodiode chip to connect an external optical communication system to the optical element.
Particularly, the present invention also relates to a method for manufacturing a laser diode chip which is used to convert electric signals into optical waves in the communication system using optical fibers.
Further, the present invention relates to a method for aligning the positions between a laser diode chip and an optical fiber as well as between a photodiode chip and an optical fiber in the optical fiber communication system.
For an optical communication, an optical transmitting module to convert electric signals into optical signals for transmitting as well as an optical receiving module to convert optical signals into electric signals for receiving are essential.
In addition, the art with which a variety of optical elements for generating, detecting, modulating and distributing functions of a light are attached with optical fibers and packaged is essential for commercializing all sorts of communicating elements.
In the process for packaging optical modules, one of the most difficult and costly steps is that of aligning and fixing an optical fiber in the wave guiding path of an optical element which represents a determinant factor for the cost of an optical communication module.
That rests on the difficulty in spatially aligning an optical element and an optical fiber, and holding the both in the aligned position without displacement in view of the very small area for the optical input or output of an optical element in the order of a few square micrometers and also the small area for the optical input or output of an optical fiber in the order of several tens of square micrometers.
The conventional methods for aligning an optical transmitting module and an optical receiving module may be broadly divided into an active aligning method and a passive aligning method.
However, the active aligning method has a difficulty in cost reduction because it needs a long processing time and many parts due to the use of lenses and an expensive laser welder.
On the other hand, the passive aligning methods can be performed without the use of those lenses and laser welders and therefore are coming to the front as new methods for reducing the price of the optical communication modules.
According to a conventional passive aligning method as shown in FIG. 14, after the chip marker 1022 on the bottom surfact of a laser diode chip 1010 is caused to match the substrate marker 1014 on the top surface of a substrate 1000, the laser diode chip 1010 is bonded to the metal junction layer 1012 of the silicon substrate 1000 by using a flip chip bonder.
The method using markers as described above is not much more advantageous in the point of the required time for process as compared to the active aligning method and also has a drawback of an increased installation cost for the equipment like a flip chip bonder.
Another conventional passive aligning method is shown in FIG. 15.
In this method, first a support 2040 loaded with a laser diode chip 2010 is fixed bonded on the surface of a substrate 2030 and then mounts 2050 and 2060 are fixed to the substrate 2030. Subsequently, the optical fiber 2020 is caused to be received, with its end close to the laser diode chip 2010, in the groove 2051 formed on the mount 2050 and then the optical fiber 2020 is aligned in its position with regard to the laser diode chip 2010 by adjusting the position of the end of the optical fiber 2020, which end positions on the side of the mount 2050. When the optical fiber 2020 has been precisely aligned in position through those procedures, the optical fiber 2020 is fixed to the mount 2060, for example, through soldering.
For the optical communication module according to FIG. 15 as described above, the positions in which the mounts and the support will be fixed are not exactly determined and therefore a great deal of time is spent to find optimum fixing positions at the time of mounting work. Nevertheless there arise deviations in the fixing positions depending on the individual products because the mounts or the supports are not exactly positioned.
Accordingly, the position alignment operation for the optical fiber with regard to the laser diode chip is not only difficult but the fixing positions of the mounts and supports with unduly high errors can also cause the problem that the optical fiber is not properly lined up with the axis of the laser diode chip.
An improved optical communication module intended to solve the above-described problem is disclosed in the Korean Patent Application No. 1997-044417.
Referring to FIG. 16 concerning the corresponding art, the art is characterized in that the position determining means 3091, 3092 and 3093 to define the positions in which the support 3040 and the mounts 3050 and 3060 are to be fixed are provided.
In particular, the support 3040 on which the laser diode chip 3010 is mounted is inserted into the first position determining groove 3091 on the substrate 3030 and fixed there through bonding or the like. Then, the mount 3050 is inserted into the second position determining groove 3092 and the mount 3060 is inserted into the third position determining groove 3093 on the substrate 3030 and then fixed through bonding.
Subsequently, after the optical fiber 3020 is placed on the mount 3050 with its end close to the laser diode chip 3010 received in the groove 3051, the optical fiber 3020 is brought into a correct position for alignment with the laser diode chip 3010 by adjusting the position of the optical fiber 3020 at its end part on the side of the mount 3050.
When the optical fiber 3020 has been precisely set in its desired position, the optical fiber 3020 is fixed to the mount 3060 through soldering or the like.
Because the support 3040 and the mounts 3050 and 3060 are fixed after they were inserted into their respective position determining grooves 3091, 3092 and 3093 in the assembling operation as described above, even in the case of mass production of optical communication modules, the positions of the support 3040 and the mounts 3050 and 3060 relative to that of the substrate 3030 can always be maintained definite.
The primary object of the present invention is to provide a process for manufacturing laser diode chips on a large scale, which diodes can be controlled within the order of xc2x11 micron in the tolerance of size, through an etching step.
The second object of the present invention is to improve the structure of a silicon substrate on which an optical fiber and a laser diode chip are positioned so that the optical fiber and the laser diode chip can be exactly aligned with each other.
The third object of the present invention is to provide a passive aligning method for an optical communication module which permits a precise positioning of an optical fiber and a laser diode chip on a substrate.
The fourth object of the present invention is to reduce the manufacturing cost for an optical communication module by enabling an optical fiber and a laser diode chip to be aligned in a passive manner on a silicon substrate without the use of high-priced bonding equipment.
The fifth object of the present invention is to improve the construction of a silicon substrate on which an optical fiber and a photodiode chip is positioned so that an exact alignment of the optical fiber with the photodiode chip can be achieved.
The sixth object of the present invention is to provide a passive method for aligning an optical receiving module which permits an exact positioning of an optical fiber and a photodiode chip on a silicon substrate.
The seventh object of the present invention is to reduce the cost for manufacturing an optical receiving module through aligning an optical fiber and a photodiode chip on a silicon substrate in a passive manner without the use of an expensive boding equipment.
Finally, the eighth object of the present invention is to improve the exactness of packaging process and to reduce the required time in making the optical transmitting module and the optical receiving module packagable.
The above described objects are achieved by a method for manufacturing a laser diode chip according to an embodiment of the invention which comprises the steps of: (1) vapor-depositing a nitride thin film(Si3N4) on the surface of a wafer on which the n type InP, p type InP, n type InP, p type InP and InGaAs layers are successively laminated with the completion of the tertiary MOCVD growth, and etching the InGaAs layer by using the mixed solution of sulfuric acid, hydrogen peroxide and distilled water after opening an etching window by means of photolithography to form V-grooves as cutting sites with a view to control the size of laser diode chip within xc2x11 micron ; (2) etching an InP layer as a current cut-off layer by using a solution based on a hydrochloric acid; (3) vapor-depositing a nitride thin film(SiNx) by using a PECVD process; (4) opening the electrode forming window to form electrodes by means of a photolithography and forming P type electrodes on the surface of the wafer; (5) forming a N type electrode on the back surface of the wafer after polishing the back surface of the wafer and (6) manufacturing laser diode chips having a desired size by cutting the V-grooves on the chip set with a breaker, when the laser diode chip set with V-grooves is completed through the above described steps of (1) to (5).
The above described objects are also achieved by an optical transmitting module according to another embodiment of the invention which consists of a silicon substrate, an optical fiber fixed to the substrate and a laser diode chip, with the first fixing groove for supporting and fixing the optical fiber, with the second fixing groove for supporting and fixing the laser diode chip and with a mediating groove for positioning the optical fiber and the laser diode chip at a definite distance, said mediating groove being formed between the first and the second grooves, all those grooves being formed on the top side of said substrate, wherein the first and the second fixing groove are each formed in their predetermined depths on the top side of the substrate so that the central axis of the optical fiber exactly may agree with the center of optical beams from the laser diode chip, the optical fiber and the laser diode chip being received in the first and the second groove, with the result that the relation of mutual positions for the optical fiber and the laser diode chip is precisely determined merely by seating the optical fiber and the laser diode chip in the first and the second groove.
The above described objects are also achieved by a method for aligning an optical transmitting module according to another embodiment of the present invention which comprises the steps of: preparing a laser diode chip manufactured by the method defined in claim 1, in order to form the first fixing groove for fixing an optical fiber, the second fixing groove for fixing a laser diode chip and a mediating groove for connecting the first and the second fixing groove on the top surface of a silicon substrate, forming patterns corresponding to those grooves by using a photolithography, etching the first fixing groove, the second groove and the mediating groove by using potassium hydroxide solution, forming metal patterns on the first fixing groove and the second fixing groove, each formed by etching process, positioning the optical fiber and the laser diode chip in the first and the second fixing groove formed with the metal patterns, followed by fixing of the fiber and the chip.
The above described objects are also achieved by an optical receiving module according to still other embodiment of the present invention which consists of a silicon substrate, an optical fiber fixed to the substrate and a photodiode chip, with the first fixing groove for supporting and fixing the optical fiber, with the second fixing groove for supporting and fixing the photodiode chip and with a mediating groove for positioning the optical fiber and the photodiode chip at a definite distance, said mediating groove being formed between the first and the second groove, all those grooves being formed on the top side of said substrate, wherein the first and the second fixing groove are each formed in their predetermined depths on the top side of the substrate so that the light emitting from the optical fiber can be transmitted to the photodiode chip without loss, with the result that the relation of mutual positions for the optical fiber and the photodiode chip is precisely determined merely by seating the optical fiber and the photodiode chip in the first and the second groove.
The above described objects are also achieved by a method for aligning an optical receiving module according to still other embodiment of the present invention which comprises the steps of: in order to form the first fixing groove for fixing an optical fiber, the second fixing groove for fixing a photodiode chip and a mediating groove for connecting the first and the second fixing groove on the top surface of a silicon substrate, forming patterns corresponding to those grooves by using a photolithography, wherein the pattern for the mediating groove is so formed that the mediating groove extends perpendicular to the optical axis, etching the first fixing groove, the second groove and the mediating groove by using potassium hydroxide solution, wherein the second fixing groove is formed in such a manner that its bottom surface lies a little higher than the base surface of the first fixing groove, forming further a laser beam guiding slot, which extends in line with the first fixing groove and which has its base at the same elevation as the first fixing groove, on the central area of the bottom surface of the second fixing groove, forming metal patterns on the first fixing groove and the second fixing groove, and seating the optical fiber with its bottom surface in the first fixing groove, followed by fixing thereof and seating the photodiode chip with its bottom surface in the laser beam guiding groove, followed by fixing thereof.
The present invention allows the use of simpler equipments and a passive type alignment method for speedy alignment mainly through the enabled control of the size of the laser diode chip within 1 micron thanks to cutting of laser diode chips under the use of etching process.
The present invention, wherein individual laser diode chips are formed from the chip set through a step of etching and V grooves are formed on the silicon substrate for alignment of the laser diode chip, does not need provision of markers for the purpose of alignment as in the conventional art and permits use of an ordinary die bonder for mounting the laser diode chip, whereby the reduction in the required processes and the saving in the installation cost of equipments are achieved.
Furthermore, the present invention, in which a groove is already provided to receive a photodiode chip, contrary to the conventional art, and a direct and ready mounting of a photodiode chip on a silicon substrate is possible, has the advantage of lesser constituting parts and simpler process as compared to the prior art.
Other objects and advantages of the invention will be understood from the following description of some preferred embodiments.